THE BILLIONAIRES' NEST: Meet The Tycoons Who Work In New York's Iconic GM Building

In 2008, developer Harry Macklowe was faced with $7 billion in debt and was forced to give up his crown jewel, the 50-story, 1.82 million-square-foot GM Building at 767 Fifth Avenue. A group led by Boston Properties' Mort Zuckerman paid $2.8 billion for the tower, about twice what Macklowe had paid just five years earlier.

But last year, when the families of two billionaires, Soho China's Zhang Xin and Brazilian banking magnate Moise Safra, bought a 40 percent stake in the building, its value had shot up to $3.4 billion, making it the most expensive office tower in the country.

"It's probably one of the most recognizable assets in the world," said Greg Kraut, a principal at commercial brokerage Avison Young. Kraut added that the property was one of the only buildings in the Plaza District with floor plates large enough to support the bigger hedge funds. "Once you manage more than a couple billion dollars worth of assets, you can't be on 10,000-square-foot floor plates," he said.

This month, The Real Deal broke down just which companies occupy the trophy tower. Hint: billionaire bold-faced names abound.

CoStar Group data shows that there are currently over 90 tenants at the property, which is anchored by the white-shoe law firm Weil, Gotshal & Manges and cosmetics giant Estée Lauder. But the building is also home to some of the world's most high-profile private equity firms, with founders including billionaires Carl Icahn and J. Christopher Flowers. And according to website Hedge Tracker, the address was home to eight of the world's top 100 hedge funds in 2012.

CBRE Group, which handles leasing at the property, referred questions to Boston Properties, which did not respond to requests for comment.

On the following page is a look at some of the building's most noteworthy tenants.